1. Field of the Invention
The present invention relates to a reclamation method of a semiconductor wafer, more specifically, a reclamation method of a semiconductor wafer in which the number of reclamation cycles can be increased.
2. Description of Related Art
In a device forming process, a variety of inspections are performed in a variety of important processes of operation by using test wafers. The test wafers are obtained from a same ingot from which silicon wafers shipped from a wafer fabrication plant are obtained. In the device forming process, defective wafers are produced in each process of operation, representing about 30% of the entire processed wafers. The test wafers and defective wafers are generally transferred to a reclamation line, instead of being disposed of, and then recycled as reclaimed polished wafers having an equivalent level to new wafers (refer to Related Art 1, for example). Wafer reclamation described above is considered to be performed more frequently for wafers having larger diameters, such as, for example, silicon wafers having a diameter of 450 mm and the like.
Silicon wafers used as reclamation material vary in type. Examples of the silicon wafers include but are not limited to bare wafers, wafers having an oxide film, wafers having a nitrogen film, wafers having a polysilicon film, diffused wafers, epitaxial wafers, resist-coated wafers, metal-coated wafers, patterned wafers, wafers having a multilayer film, and the like. In a conventional reclamation process, silicon wafers received as reclamation material undergo incoming inspections, such as sorting by film type, an appearance inspection, and the like. Then, the silicon wafers sequentially undergo grinding of a front surface, on which various films and devices are formed; mirror-polishing of a wafer external peripheral surface; and mirror-polishing of the front surface.
[Related Art 1] Japanese Patent Laid-open Publication No. 2000-269174
In the conventional wafer reclamation process, as described above, the front surface of the wafer is ground to remove a variety of films, including an oxide film, and devices formed thereon. Thus, the more the number of reclamation cycles of a silicon wafer is, the thinner the wafer is on the front surface side from grinding in each reclamation cycle. As a result, a chamfer width on the front side of the wafer is narrowed, and thus effectiveness is reduced in forming a chamfered portion on the front side of the wafer. Problems occur accordingly, inducing chipping in the external peripheral portion of the wafer at the time of polishing of the front surface of the wafer, and wafer cracking in a device forming process. In addition, repeated reclamation of the silicon wafer may result in deformation in the chamfered portion of the wafer due to external periphery sagging and the like at the time of polishing of the silicon wafer. In order to prevent the problems, the number of wafer reclamation is conventionally limited to only a few times.